The effect of heat in conjunction with x-ray on jejunum (crypt colony assay and LD50/6) spinal cord (myelitis) and two transplantable mammary tumors is being studied in a murine model. Microwave heating is being used where feasible. Heat for 5 min at 44 degrees C followed in 5 min by x-ray is the treatment standard for all assays. Thermal enhancement ratios will be determined and therapeutic gain factors calculated.